When his daughter got sick, he made a vaccine and saved millions of lives in the process.

On March 21, 1963, Maurice R. Hilleman's daughter woke him up. She had a sore throat.

When he examined her, he realized that she had swelling beneath her jaw.

He knew immediately that this was no ordinary sore throat. She had mumps.

Mumps is a contagious viral disease that typically starts with a fever, headache, aches and pains, fatigue, and a loss of appetite. It is then followed by swollen salivary glands. It used to be the most common cause of acquired hearing loss, and there was no treatment.

It's easy to forget today that those severe childhood diseases like mumps were once a relatively common occurrence.

As recently as half a century ago, kids would often get sick with diseases that caused devastating side effects and, sometimes, even death. In fact, some illnesses such as mumps, measles, and rubella were so prevalent that most parents could easily recognize them — usually because they had either had them themselves or had seen them before.

Measles — the same disease blamed partly for decimating Native American populations after the arrival of European explorers — was so common at the beginning of the 20th century that almost all Americans caught it sometime during their lifetime (though usually as children). In 1912-22, an average of 6,000 people died from it each year in the U.S.

So when Hilleman's daughter got sick, he decided to take the only action he could. He went to work.

Hilleman had a Ph.D. in microbiology from the University of Chicago, and he had been working at Merck & Co. for about six years, leading the company’s virus and vaccination research programs.

So, after she was in bed, he immediately drove to work, picked up sampling equipment from his lab, and went home to collect a swab from the back of her throat. He then brought the sample back to the lab, where he used it to help develop a vaccine against mumps.

Hilleman and his colleagues used the sample from his daughter to isolate the disease organism and figure out how to keep it alive in the lab. Then they tried to weaken it in a process called attenuation, or passing the virus over and over through a series of cells until it can no longer reproduce inside a human being (or make people sick) but can still make the body's immune system react and produce antibodies and T-lymphocytes (a type of white blood cell).

‌Illustrations that were used in public service announcements to encourage parents to vaccinate their children against rubella in the late 1960s and early 1970s. Image via the Centers for Disease Control and Prevention. ‌

But his work on vaccines didn’t stop there. In 1968, he improved upon an existing measles vaccine (one that still caused rashes and fevers). In 1969, he worked with federal regulators to develop a vaccine for rubella in order to prevent another epidemic.